The present invention relates to novel coloring phthalide compounds, a method of producing the compounds, and recording materials using any of the phthalide compounds as coloring component, which recording materials are capable of producing images having light absorbancy in the near infrared region by thermosensitive recording, pressure-sensitive recording or by use of laser beams, or the like.
A conventional pressure-sensitive recording material utilizes a chemical reaction between a colorless or light-colored leuco dye and a color developer capable of inducing color formation in the leuco dye to form colored images. More specifically, the pressure-sensitive recording material comprises (i) a coloring leuco dye sheet coated with a leuco dye which is dissolved in an organic solution and microcapsuled and (ii) a color developer sheet coated with a color developer for the leuco dye and a binder agent. The coloring leuco dye sheet is superimposed on the color developer sheet and pressure is applied thereto in such a manner that the microcapsules containing the leuco dye are ruptured so as to react with the color developer.
A conventional thermosensitive recording material generally comprises a support such as paper, synthetic paper or plastic film, and a thermosensitive coloring layer comprising as the main components a leuco dye and a color developer capable of inducing color formation in the leuco dye upon application of heat thereto to form colored images. The application of heat for such image formation is carried out, for instance, by use of minute heat generating resistance elements, such as a thermal head and a thermal pen.
These pressure-sensitive and thermosensitive recording materials are widely used because recording can be carried out more speedily by using a relatively simple device, without the necessity for complicated processing such as development and fixing of images, as compared with the recording materials for electrophotography and electrostatic recording.
Conventionally employed representative leuco dyes for use in such recording materials are Crystal Violet Lactone and Leuco Crystal Violet which are for blue-coloring, and fluorane compounds having an anilino substituent at is 3 position and an anilino substituent at its 7 position which are for black coloring.
Recently optical character-reading apparatus have been developed, for example, for reading bar codes in bar-code labels, and are used in a variety of fields. In these apparatus, light sources emitting light having a light wavelength of 700 nm or more, such as a light emit diode and a semi-conductor laser, are in general use. However, the above-mentioned leuco dyes, when colored blue or black, scarcely absorb the light in the near infrared region having a wavelength of 700 nm or more, so that the reading of the developed color is not possible with the above-mentioned recording apparatus.
Accordingly, there is a strong need for the development of a new leuco dye for which the optical absorbancy wave length of the color forming material is greater than 700 nm.
Examples of such a leuco dye are the monovinyl coloring phthalide compounds disclosed in Japanese Laid Open Patent Application Nos. 51-121037 and 57-167979. These compounds, in comparison with the compounds which do not have a monovinyl group, have an absorbancy greater than the 750 nm vicinity and can exhibit absorption in the near infrared region. However, their absorbancy in the region greater than 750 nm is very weak so they do not fulfil the requirements for such a material.